The purpose of this proposal is to identify critical idiotopes in anticentromere (ACA) and antitopoisomerase I (antitopo I) from SSc absent in RD that may predict which patients will develop SSc. In addition, in long range it would be possible to target these idiotopes and control the expression of SSc. The hypothesis of this grant is that ACA and antitopo I Ids from SSc differ from the RD Ids. This proposal plans to 1) determine whether the SSc antitopo I and ACA utilize preferential Ig gene families with or without somatic mutations 2) determine whether RD antitopo and ACA are the product of randomly used genes, 3) locate a critical idiotope that defines the binding of antitopo Id to its anti-Id and to antigen, and 4) identify the role played by this idiotope in the idiotypic network dysregulation in mice. In order to do this, ACA and antitopo I secreting B cell clones from SSc and RD will be established and used to determine their immunoglobulin heavy chain variable (VH) region genes. The specific SSc-VH sequence will be expressed in baculovirus to determine the % inhibition of binding of polyclonal SSc autoantibodies to antigen and anti-Id compared to RD autoantibodies. The sequences of the framework (FR) and complementary determining regions (CDRs) from RD will be exchanged for the corresponding SSc-VH sequences. This RD-modified VH will be used as control to identify an idiotope critical to the antigen and anti-Id binding specific for the SSc autoantibodies. Mice will be immunized with a) the recombinant SSc-VH or b) the recombinant RD-modified VH, and emergence of autoantibodies or SSc manifestations will be studied. The proposed work will be done at the University of Connecticut Health Center, Division of Rheumatic Diseases where all the facilities and equipment necessary for this work are available, as well as advice from senior immunologists and rheumatologists who are part of the Division.